-- 按照给定的字节长度截取最大可能的中英文混合字符串，避免了半个汉字的问题
create or replace function substr_gb(str_    varchar2,
                                     begin_  integer,
                                     length_ integer) return varchar2 is
    result varchar2(256);
begin
    if length(substrb(str_, begin_, length_)) =
       length(substrb(str_, begin_, length_ + 1)) then
        result := substrb(str_, begin_, length_ - 1);
    else
        result := substrb(str_, begin_, length_);
    end if;
    return result;
end substr_gb;